Estimation of resonance characteristics of single-layer surface-plasmon sensors in liquid solutions using Fano's approximation in the visible and infrared regions

In this work, we consider the use of planar sensing structures, which support excitation of surface plasmon polarition (SPP) modes, for detecting changes in solvents, i.e. water, ethanol, isopropanol. In the structures under study, SPP modes propagate along the interfaces between metals and general solvents. The analysis of characteristics of the resonance response is based on Fano’s approximation within the coupled-mode theory in the visible and infrared regions. The maximum sensitivity and field enhancement are revealed in the near- and mid-infrared regions in the case of ethanol and isopropanol, which enables sensing applications beyond the regions of water absorption.